1. Field of the Invention
The present invention relates to an imaging device, a GPS control method, and a computer program. More specifically, the invention relates to an imaging device, a GPS control method, and a computer program that each implement, for a device that executes position measurement by employing a global positioning system (GPS), drive control of the GPS depending on the frequency of execution of imaging processing to thereby realize reduced power consumption.
2. Description of the Related Art
In recent years, imaging devices such as video cameras and still cameras equipped with a global positioning system (GPS) function have been proposed and used. These imaging devices acquire position information and record the acquired position information as attribute information of imaging data.
In such application products of the GPS technique, a GPS reception module is typically supplied with power so that signals from satellites are continuously received and analyzed when the apparatus is being used in general. However, imaging devices such as video cameras and still cameras employ a cell as a power source, and hence it is an important challenge for these imaging devices to suppress power consumption.
For an apparatus that employs a cell as its power source and includes a GPS reception module, continuous supply of power to the GPS reception module leads to a problem that excessive power consumption is caused and therefore the cell is exhausted soon. As one of solutions to reduce this power consumption, a system would be available that employs execution of the necessary minimum energization for the GPS reception module, such as intermittent energization and intermittent driving therefor. However, the intermittent driving causes a problem that the waiting period from activation of the GPS module until acquisition of position information is increased.
To decrease the waiting period until position acquisition, it is necessary to effectively utilize navigation message information of a GPS satellite, called navigation data and received by the GPS module from the satellite, to thereby complete satellite acquisition, i.e., processing of reception of electric waves from the satellite, in a short period. However, navigation messages have the expiration time defined as the validity period (validity periods of almanac data and ephemeris data included in navigation messages are three months and two hours, respectively).
In a configuration that continuously receives navigation messages, constant data updating is allowed and thus navigation messages (almanac data and ephemeris data) within the validity period are stored so that rapid satellite acquisition is permitted by use of the stored navigation messages. However, when the above-described intermittent driving is implemented, there is a case where data recorded in the GPS module has expired. In this case, efficient satellite acquisition by use of these data cannot be carried out, execution of a satellite acquisition process that takes comparatively long processing time is requisite. As a result, the period from activation of the GPS module to acquisition of position information is greatly extended, which possibly causes a problem that timely position information cannot be acquired.
For example, in a configuration in which a GPS module is provided for a video camera or still-image camera and processing for adding position information acquired from the GPS module as attribute information of imaging data is executed, it is requisite to obtain accurate position information at the timing when a user starts imaging. However, if the period from activation processing to acquisition of position information is extended due to the above-described intermittent operation, a problem that accurate position information corresponding to imaging data cannot be obtained occurs.